VSS

Volume Shadow Copy service (VSS) is a software service introduced by Microsoft on Windows operating systems. This service collaborates with the backup application, applications to be backed up, shadow copy providers, and the operating system kernel to implement the management of volume shadow copies and shadow copy sets.

The idea of the Volume Shadow Copy service is to provide a unified communication interface that can coordinate backup and restore of any application regardless of their specific features. With this approach, a backup application does not need to handle each application to be backed up specifically. However, this approach is applicable to a backup application only in case it conforms to the VSS specification.

What is a shadow copy?

A shadow copy refers to a volume that represents a duplicate of the original volume at a particular moment in time. The volume shadow copy technology provides a copy of the original volume at a certain point in time. The data is then backed up from the shadow copy, not from the original volume. The original volume continues to change as the backup process continues, but the shadow copy of the volume remains constant.

Shadow copy is basically a snapshot backup, which allows applications and users to continue writing to data volumes, even if they are in the middle of a backup process, while the backup is getting data from a shadow copy of the original volume.

A shadow copy set is a collection of shadow copies created in the same point in time.

What is a writer?

A writer refers to any process that initiates change of data on the original volume. Writers are typically applications (for example, MSDE Writer for MS SQL Server) or system services (for example, System Writer and Registry Writer) that write persistent information on a volume. Writers participate in the shadow copy synchronization process by assuring data consistency.

What is a shadow copy provider?

A shadow copy provider refers to some entity that performs the work involved in creating and representing the volume shadow copies. Shadow copy providers own the shadow copy data and expose the shadow copies. Shadow copy providers can be software (including a system provider, MS Software Shadow Copy Provider) or hardware (local disks, disk arrays).

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HP B6960-96035 manual What is a shadow copy?, What is a writer?, What is a shadow copy provider?